This invention relates generally to the field of telephony, and more particularly to an improved form of telephone circuit module incorporating means for automatically switching bridged subscriber lines without the necessity of providing large tie jumpers and prior art saturable bridge lifter devices.
Although saddled with a degree of inconvenience from the standpoint of an individual subscriber, bridged subscriber circuits, commonly referred to as party lines, are still in wide use throughout the United States. In such connections, two or more individual subscriber lines share a common input and assigned telephone number, and where one of the bridged circuits is in use, the others are necessarily inoperative. In the traditional form of interconnection, several lines are connected from the connector block to a known saturation type bridge lifter which, in turn, connects the line in use to a terminal block and office switching equipment. The saturated type bridge lifter is a separate unit mounted upon the main distributing frame, and requires relatively long and costly cable runs when assembling the circuits on the main distributing frame. Apart from the cost of such devices, they occupy considerable space on the distributing frame, which might otherwise be more efficiently utilized.
As might be expected in the case of a long-standing problem, considerable progress has been made in the art. A solid state bridge lifter circuit has been developed of size sufficiently small to permit mounting within the housing of a plug type protector module used to protect an individual subscriber line against the effects of overload. With more modern type connector blocks utilizing plug type protector modules, reassignment of central office lines is simply a matter of replacing existing protector modules with protector modules incorporating the solid state bridge lifter circuit. The resulting advantages include the saving of frame space, simplified administration, and savings in installation costs.
Unfortunately, many older telephone offices, having older type frame and connector block installations, are unable to use the above-described structure for the reasons that the older style connector blocks employ protector devices which are not enclosed within a replaceable module. A typical example is the Western Electric Type C-50A or C-52A protector. The usual heat coil and carbon arc components are exposed and are mounted in operative position by resilient conductive spring blades having no means for accommodating the bridge lifting circuitry. In the recently issued U.S. Pat. No. 4,237,346 granted to Paul V. De Luca et al., and assigned to the same assignee as the instant application, there is disclosed a structure which solves this problem.
A somewhat similar problem is encountered in the case of telephone offices of somewhat newer vintage employing the Western Electric Type 300 which were widely installed during the 1950 decade. This type block is somewhat more self-contained than the Type C-50A, but does have exposed pairs of wire wrap terminals along one side which offer a location in which the bridge lifter module may be placed in series with a subscriber line at the terminal block.